The vibrational spectra of phosphate modes for GDP and GTP bound to the c-Harvey p21(ras) protein have been determined using 18O isotope edited Raman difference spectroscopy. A number of the phosphate stretch frequencies are changed upon GDP/GTP binding to ras, and the results are analyzed by ab initio calculations and through the use of empirical relationships that relate bond orders and bond lengths to vibrational frequencies. Bound GDP is found to be strongly stabilized by its interactions, mostly electrostatic, with the active site Mg2+. Bound GTP also interacts with the active site Mg2+ via its beta-phosphate group, as expected on the basis of crystallographic studies of bound GppNp. The angle between the nonbridging P&bondDot;O bonds of the gamma-phosphate of bound GTP increase by about 1-2 degrees compared to its solution value, thus bringing about a geometry that is closer to planar for these bonds as expected for the putative pentacoordinated transition state geometry of the phosphotransfer reaction. Modeling of the interactions at the nucleotide binding site suggests that the water molecule in-line with the P-O bond is positioned to bring about the change in bond angle. Moreover, a weak fifth bond (about 0.03 vu) appears to be formed between it and the gamma-phosphorus atom of bound GTP with a concomitant weakening of the O-P bond between the GDP leaving group and the gamma-phosphorus atom. Hence, an important role of the active site structure appears to be the strategic positioning of this in-line water. These structural results are consistent with a reaction pathway for GTP hydrolysis in ras of synchronous bond formation between the gamma-phosphorus of GTP and the attacking nucleophile and bond breaking between the gamma-phosphorus and the GDP leaving group.

Lignin-based dithiocarbamate (LDTC) was synthesized by anchoring the chelating agent of dithiocarbamate to the ortho sites of phenol hydroxyl groups in the alkaline lignin matrix. The LDTC biomaterial was characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and elemental analysis. Due to the cross-linked polymer matrix, high content of dithiocarbamate groups and excellent complex ability, the LDTC was used as a new bio-adsorbent for the removal of metallic ions from aqueous solution. The influences of pH, LDTC dosage, contact time, and initial metallic ion concentration on adsorption capacity and competitive adsorption of multi metallic ions have been investigated. The regeneration of LDTC was also studied. The results demonstrated that LDTC showed fast adsorption, higher adsorption capacity and feasible regeneration compared to other lignin-based bio-adsorbents even activated carbon. The adsorption kinetics and adsorption isotherms were fitted well by a pseudo second-order model and D-R model, respectively. Moreover, the resultant metal-loaded solid bio-sorbents (LDTC-M) were firstly estimated as free radical scavengers due to the inherent merits of naturally occurring polyphenols which therefore could provide a potential way for value-added usage of the LDTC-M.

The development of ecofriendly sorbents for fast and efficient removal of heavy metals from aqueous media still remains a significant challenge. Here, we report that this task can be addressed by creating a porous naturally occurring polymer, as illustrated by functionalizing lignin with large numbers of mesopores and functional groups. We show that surface-functionalized porous lignin (SFPL), obtained by a two-step process, has a large surface area of 22.3 m2/g, 12 times that of lignin, and a high density of dithiocarbamate groups (2.8 mmol/g). SFPL was found to exhibit an excellent adsorption performance toward lead ions dissolved in water. For example, 99% of the lead ions from 50 mL of a solution containing 20 mg/L lead ions was removed in just 30 min by 0.01 g of SFPL. The saturated adsorption capacity of SFPL for lead ions was found to be 188 mg/g, which is 13 times that of the original lignin and 7 times that of activated carbon. The adsorption process is endothermic and involves intraparticle diffusion and chemical adsorption between lead ions and the functional groups of SFPL. The cost effectiveness and environmental friendliness of SFPL make it a promising material for removing lead and other heavy metals from wastewater.

Raman and infrared spectra were examined for guanosine 5′‐diphosphate (GDP) and guanosine 5′‐triphosphate (GTP) in aqueous solution. The vibrational modes were assigned on the basis of isotopic frequency shifts and relative intensities in the Raman and infrared spectra. The observed frequency shifts on 18O isotope labeling made it possible to identify the bands from each phosphate group (α, β, γ). Frequency shifts were observed as Mg2+ complexes with GDP and GTP. The results suggested that Mg2+ binds to GDP in a bidentate manner to the α, β P · · O bonds and in a tridentate manner to the α, β and γ P · · O bonds of Mg·GTP. The results indicate that structure of Mg2+ coordinated to GTP in aqueous solution differs somewhat to that found for Mg·ATP. © 1998 John Wiley & Sons, Inc. Biospectroscopy 4: 219–227, 1998